1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device. More particularly, the present invention relates to a method of fabricating a CMOS (Complementary Metal Oxide Silicon) image sensor including an inner micro-lens.
2. Description of Related Art
A method of fabricating a CMOS image sensor according to a related art is shown in FIGS. 1A to 1G. FIGS. 1A to 1E show the procedure for forming an outer micro-lens on a substrate having a logic block, a light receiving device, etc.
FIG. 1A shows a device protective layer 120 coated on a substrate 100 formed with a light receiving device 110, such as a photodiode. Then, referring to FIG. 1B, after coating an aluminum metal layer (not shown), an aluminum interconnection 130 is formed through photo and etching processes, and then an interlayer dielectric layer 140 is coated thereon.
After that, referring to FIG. 1C, a Si3N4 layer or a SiO2 layer 150 is deposited to form an inner micro-lens. In addition, although not shown in FIG. 1C, photoresist is coated on the Si3N4 layer or the SiO2 layer 150. Then, a thermal reflow process is performed to form a dome shape.
Then, an anisotropic etching process is performed in the vertical direction until the photoresist as well as a predetermined portion of the Si3N4 layer or the SiO2 layer 150, in which the photoresist is not formed, have been completely removed. Thus, as shown in FIG. 1D, a dome-shaped inner micro-lens 155 including Si3N4 or SiO2 is formed.
In addition, as shown in FIG. 1E, an oxide layer 160 is formed on the inner micro-lens 155. Then, a color filter 170 and a planarization layer 180 are formed on the oxide layer 160.
Finally, as shown in FIG. 1G, an outer micro-lens 190 is formed on the planarization layer 180 through a photo process.
According to the CMOS image sensor having the above structure, the light focusing function of the micro-lens may exert an influence upon the quality of the image sensor. In order to effectively focus the light, the curvature of the micro-lens must be uniformly formed such that the light can be constantly focused onto the light receiving device. However, the above-mentioned conventional CMOS image sensor employs the inner micro-lens, which is formed through the anisotropic etching process instead of the photo process, it is very difficult to uniformly set the curvature of the inner micro-lens. In addition, the process of forming the inner micro-lens is very complicated. Accordingly, the product yield is lowered and the manufacturing cost for the CMOS image sensor may rise.